The malignant process and the treatment of cancer by chemotherapy and radiotherapy will be studied in the laboratory using three interrelated approaches: 1) Theoretical, methodological, and experimental work will continue on the kinetic analysis of growth of solid tumors at the gross and cellular level. Confidence limits will be sought for estimates of the cell cycle, growth fraction, growth rate, and rate of tumor cell loss for tumors in general and C3H mouse mammary tumors in particular. 2) We will attempt to identify the nonproliferating tumor cell, to isolate it in bulk, and to study its biological properties. Autoradiography, cytophotometry, and fluorometry with a flow system will be used to explore the nature of chromatin and to identify and sort nonproliferating cells in populations of aging cells and solid tumors. 3) A new biostatistical approach toward optimizing the degree of aggressiveness of treatment strategy will be tailored to the collation of therapeutic data and the design of clinical trials.